This study is an open-label evaluation of the pharmacokinetics and intracellular metabolism of intravenous and oral Zidovudine. Pharmacokinetics and intracellular metabolism will be compared between men (n=18) and women (n=24), and among the women, before and after initiation of either oral contraceptive pills or injectable medroxyprogesterone (Depo-Provera). Plasma and genital HIV levels will also be compared in the women before and after initiation of hormonal therapy. Pharmacokinetic studies will be done on two consecutive days, one after oral and one after intravenous Zidovudine. Women will be studied in the luteal phase of the menstrual cycle, then begun on their choice of hormonal contraceptive with onset of menses. Pharmacokinetic studies will be repeated three weeks after initiation of contraception.